The present invention relates to a color cathode ray tube in which the amounts of horizontal and vertical deflection of a plurality of electron beams is individually controlled to correct coma caused by a deflection magnetic field, and convergence errors of the plurality of electron beams are suppressed to thereby obtain a good image display over the entire phosphor screen.
In a color cathode ray tube having at least an electron gun comprising a plurality of electrodes, a deflection device, and a phosphor screen (a screen having a phosphor film, hereinafter also referred to as a phosphor. film or merely referred to as a screen), the following techniques have been known as means for reproducing a good image over the entire phosphor screen.
Japanese Patent Publication No. Hei 4-52586 discloses an electron gun emitting three in-line electron beams in which a pair of parallel flat electrodes are disposed on the bottom face of a shield cup in such a manner as to be positioned above and below paths of the three electron beams in parallel to the in-line direction and to extend toward a main lens.
U.S. Pat. No. 4,086,513 and its corresponding Japanese Patent Publication No. Sho 60-7345 disclose an electron gun emitting three in-line electron beams in which a pair of parallel flat electrodes are disposed above and below paths of the three electron beams in parallel to the in-line direction in such a manner as to extend from one of facing ends of one of a pair of main-lens-forming electrodes toward a phosphor screen, thereby shaping the electron beams before the electron beams enter a deflection magnetic field.
Japanese Patent Laid-open No. Sho 51-61766 discloses an electron gun in which an electrostatic quadrupole lens is formed between two electrodes and the strength of the electrostatic quadrupole lens is made to vary dynamically with the deflection of an electron beam, thereby achieving uniformity of an image over the entire screen.
Japanese Patent Publication No. Sho 53-18866 discloses an electron gun in which an astigmatic lens is provided in a region between a second grid electrode and a third grid electrode forming a prefocus lens.
U.S. Pat. No. 3,952,224 and its corresponding Japanese Patent Laid-open No. Sho 51-64368 discloses an electron gun emitting three in-line electron beams in which an electron beam aperture of each of first and second grid electrodes is formed in an elliptic shape, and the degree of ellipticity of the aperture is made to differ for each beam path or the degree of ellipticity of the electron beam aperture of the center electron gun is made smaller than that of the side electron gun.
Japanese Patent Laid-open No. Sho 60-81736 discloses an electron gun emitting three in-line electron beams in which a slit recess provided in a third grid electrode on the cathode side forms a non-axially-symmetrical lens, and an electron beam is made to impinge on the phosphor screen through at least one non-axially-symmetrical lens in which the axial depth of the slit recess is larger for the center beam than for the side beam.
Japanese Patent Laid-open No. Sho 54-139372 discloses a color cathode ray tube having an electron gun emitting three in-line electron beams in which a soft magnetic material is disposed in fringe portions of the deflection magnetic field to form a pincushion-shaped magnetic field for deflecting the electron beams in the direction perpendicular to the in-line direction of each electron beam, thereby suppressing a halo caused by the deflection magnetic field in the direction perpendicular to the in-line direction.
FIG. 18 is a fragmentary sectional view showing an example of an electron gun for a color cathode ray tube using three in-line electron beams.
In FIG. 18, reference numeral 1 designates a first grid electrode (G1), 2 a second grid electrode (G2), 3 a third grid electrode (G3), 4 a fourth grid electrode (G4), 5 a fifth grid electrode (G5), 6 a sixth grid electrode (G6), 30 a shield cup, 38 a main lens, and K a cathode.
In this electron gun, the fifth grid electrode 5 is a focus electrode, the sixth grid electrode 6 is an anode, and the shield cup 30 is connected to the sixth grid electrode 6. In a cathode ray tube, the shield cup 30 is directed toward the phosphor screen.
FIGS. 19A and 19B are schematic sectional views of main parts for comparison of the construction of an electron gun depending upon the manner of applying focus voltages, FIG. 19A shows a fixed focus voltage type, and FIG. 19B shows a dynamic focus voltage type.
The electrode construction of the fixed focus voltage type electron gun shown in FIG. 19A is the same as that shown in FIG. 18, in which the same functional parts as in FIG. 18 are indicated by the same reference numerals.
In the fixed focus voltage type electron gun shown in FIG. 19A, a same focus voltage Vf1 is applied to electrodes 51 and 52 constituting the fifth grid electrode 5 thereof.
On the other hand, in the dynamic focus type electron gun shown in FIG. 19B, different focus potentials Vf1 and Vf2 are applied to two electrodes 51 and 52 constituting the fifth grid electrode 5, respectively. In particular, a dynamic focus voltage dVf superposed on Vf2 is applied to the electrode 52. Further, in the dynamic focus type electron gun, a portion of one electrode extends into the interior of another electrode as indicated at reference numeral 43, which has disadvantages in that its construction is complicated as compared with the electron gun shown in FIG. 19A, the cost is high, and its workability in assembly of the electron gun is inferior.
FIGS. 20A and 20B are explanatory views of focus potentials applied to the electron guns shown in FIGS. 19A and 19B. FIG. 20A shows a focus voltage waveform for the fixed focus voltage type electron gun, and FIG. 20B shows a focus voltage waveform for the dynamic focus voltage type electron gun.
In FIG. 20B, there are a fixed focus voltage Vf1 and a voltage having a waveform of a dynamic focus voltage Vf2 superposed on another fixed focus voltage Vf20. Therefore, in the dynamic focus voltage type electron gun shown in FIG. 19B, two high-voltage lead-in pins are needed at a stem of a cathode ray tube for supplying two focus voltages, and more consideration to insulation from other adjacent stem pins is necessary than in the fixed focus type electron gun. This poses problems in that a socket of a special construction is needed for a cathode ray tube installed in a TV set, and in addition to two fixed focus voltage sources, a dynamic focus voltage generating circuit is necessary, and additional set-up time is required for adjustment of the focus voltages in the assembly line of the TV set.
Further, in the color cathode ray tube provided with the in-line type electron gun of this kind, the center electron gun is on the tube axis, but the side electron guns are offset from the tube axis so that the side electron beams travel a greater distance in the deflection magnetic field than the center electron beam, receive a larger amount of action by the deflection magnetic fields, and create rasters of a horizontally and vertically larger size on the phosphor screen than the central beam.
As a result, the rasters created by three electron beams are not coincident with each other on the phosphor screen, resulting in convergence errors.
Further, in the color cathode ray tube of this kind, when the maximum deflection angle of the electron beams is fixed, the larger the size of the phosphor screen, the longer is a distance between the phosphor screen and the main lens of the electron gun, and hence the more is focus characteristics degraded by the mutual space-charge repulsion of electrons in this region.
Accordingly, if the distance between the main lens of the electron gun and the phosphor screen is made shorter with some means, fine electron beams can be obtained as in a cathode ray tube with a small-sized phosphor screen to enhance the resolution of the color cathode ray tube.
The shortening of the distance between the main lens of the electron gun and the phosphor screen increases the deflection defocusing and deteriorate the resolution at the periphery of the screen. Therefore, in the above-described prior art, there requires the measure for further raising the dynamic focus voltage so that the technical and cost-wise burdens on the side of the image display device employing the cathode ray tube such as the increased cost of the driving circuit and the improved high voltage breakdown capacity of a socket for a cathode ray tube.
Further, the depth of the present-day TV sets depends on the overall length of the cathode ray tube, and it is preferably short considering the TV set is a kind of a furniture. Moreover, the short depth of TV sets is preferable in terms of transport efficiency for TV set makers transporting a large number of TV sets.
It is an object of the present invention to overcome various problems as noted above with respect to prior art and provide a color cathode ray tube having improved beam convergence characteristics over the entire phosphor screen by controlling horizontal and vertical coma caused by deflection magnetic fields.
In accordance with an embodiment of the present invention, there is provided a color cathode ray tube including a vacuum envelope comprising a panel portion, a neck portion, and a funnel portion connecting the panel portion and the neck portion; a phosphor screen on an inner surface of the panel portion; a shadow mask suspended closely spaced from the phosphor screen in the panel portion; an electron gun comprising a plurality of electrodes for generating and focusing three in-line electron beams and housed within the neck portion; a deflection device mounted around a transition area between the funnel portion and the neck portion for deflecting the three in-line electron beams in horizontal and vertical directions; and a convergence correction device comprising a plurality of magnetic pieces positioned on opposite sides of each of the three in-line electron beams in an in-line direction of the three in-line electron beams and disposed on a phosphor screen side of the electron gun; the plurality of magnetic pieces including a first pair of magnetic pieces positioned on a neck wall side of each of side electron beams of the three in-line electron beams in the in-line direction and a second pair of magnetic pieces positioned on opposite sides of a center electron beam of the three in-line electron beams in the in-line direction; and the first pair of magnetic pieces each having a first pair of protruding portions extending toward an adjacent one of the second pair of magnetic pieces, the first pair of protruding portions of the first pair of magnetic pieces being arranged on opposite sides of a corresponding one of the side electron beams of the three in-line electron beams in a direction perpendicular to the in-line direction; the second pair of magnetic pieces each having two second pairs of protruding portions, one of the second pairs of protruding portions extending toward an adjacent one of the first pair of magnetic pieces and the other of the second pairs of protruding portions extending toward an adjacent one of the second pair of magnetic pieces each of the second pairs of protruding portions of the second pair of magnetic pieces being arranged on opposite sides of a corresponding one of the three in-line electron beams in a direction perpendicular to the in-line direction; the first pair of magnetic pieces having a portion of an axial length greater than an axial length of the second pair of magnetic pieces; and the axial lengths being measured in a plane containing the in-line direction and a longitudinal axis of the color cathode ray tube.
In accordance with another embodiment of the present invention, there is provided a color cathode ray tube including a vacuum envelope comprising a panel portion, a neck portion, and a funnel portion connecting the panel portion and the neck portion; a phosphor screen on an inner surface of the panel portion; a shadow mask suspended closely spaced from the phosphor screen in the panel portion; an electron gun comprising a plurality of electrodes for generating and focusing three in-line electron beams and housed within the neck portion; a deflection device mounted around a transition area between the funnel portion and the neck portion for deflecting the three in-line electron beams in horizontal and vertical directions; and a convergence correction device comprising a plurality of magnetic pieces positioned on opposite sides of each of the three in-line electron beams in an in-line direction of the three inline electron beams and disposed on a phosphor screen side of the electron gun; the plurality of magnetic pieces including a first pair of magnetic pieces positioned on a neck @axe2x80x2!:l side of each of side electron beams of the three in-line electron beams in the in-line direction and a second pair of magnetic pieces positioned on opposite sides of a center electron beam of the three in-line electron beams in the in-line direction; and the first pair of magnetic pieces each having a first pair of protruding portions extending toward an adjacent one of the second pair of magnetic pieces, the first pair of protruding portions of the first pair of magnetic pieces being arranged on opposite sides of a corresponding one of the side electron beams of the three in-line electron beams in a direction perpendicular to the in-line direction; the second pair of magnetic pieces each having two second pairs of protruding portions, one of the second pairs of protruding portions extending toward an adjacent one of the first pair of magnetic pieces and the other of the second pairs of protruding portions extending toward an adjacent one of the second pair of magnetic pieces each of the second pairs of protruding portions of the second pair of magnetic pieces being arranged on opposite sides of a corresponding one of the three in-line electron beams in a direction perpendicular to the in-line direction; one of the first pair of magnetic pieces opposing one of the second pair of magnetic pieces, another of the first pair of magnetic pieces opposing another of the second pair of magnetic pieces; the first pair of protruding portions of the one of the first pair of magnetic pieces are displaced outwardly from the one of the second pairs of protruding portions of the one of the second pair of magnetic pieces in a direction perpendicular to the in-line direction, the first pair of protruding portions of the one of the first pair of magnetic pieces, and the one of the second pairs of protruding portions of the one of the second pair of magnetic pieces opposing each other, respectively; and the first pair of protruding portions of the another of the first pair of magnetic pieces are displaced outwardly from the one of the second pairs of protruding portions of the another of the second pair of magnetic pieces in a direction perpendicular to the in-line direction, the first pair of protruding portions of the another of the first pair of magnetic pieces and the one of the second pairs of protruding portions of the another of the second pair of magnetic pieces opposing each other, respectively.
In accordance with another embodiment of the present invention, there is provided a color cathode ray tube including a vacuum envelope comprising a panel portion, a neck portion, and a funnel portion connecting the panel portion and the neck portion; a phosphor screen on an inner surface of the panel portion; a shadow mask suspended closely spaced from the phosphor screen in the panel portion; an electron gun comprising a plurality of electrodes for generating and focusing three in-line electron beams and housed within the neck portion; a deflection device mounted around a transition area between the funnel portion and the neck portion for deflecting the three in-line electron beams in horizontal and vertical directions; and a convergence correction device comprising a plurality of magnetic pieces positioned on opposite sides of each of the three in-line electron beams in an in-line direction of the three inline electron beams and disposed on a phosphor screen side of the electron gun; the plurality of magnetic pieces including a first pair of magnetic pieces positioned on a neck wall side of each of side electron beams of the three in-line electron beams in the in-line direction and a second pair of magnetic pieces positioned on opposite sides of a center electron beam of the three in-line electron beams irf th@ in-line direction; and the first pair of magnetic pieces each having a first pair of protruding portions extending toward an adjacent one of the second pair of magnetic pieces, the first pair of protruding portions of the first pair of magnetic pieces being arranged on opposite sides of a corresponding one of the side electron beams of the three in-line electron beams in a direction perpendicular to the in-line direction; the second pair of magnetic pieces each having two second pairs of protruding portions, one of the second pairs of protruding portions extending toward an adjacent one of the first pair of magnetic pieces and the other of the second pairs of protruding portions extending toward an adjacent one of the second pair of magnetic pieces each of the second pairs of protruding portions of the second pair of magnetic pieces being arranged on opposite sides of a corresponding one of the three in-line electron beams in a direction perpendicular to the in-line direction; the first pair of magnetic pieces having a portion of an axial length greater than a thickness of the second pair of magnetic pieces; and the axial length being measured in a plane containing the in-line direction and a longitudinal axis of the color cathode ray tube.
In accordance with another embodiment of the present invention, there is provided a color cathode ray tube including a vacuum envelope comprising a panel portion, a neck portion, and a funnel portion connecting the panel portion and the neck portion; a phosphor screen on an inner surface of the panel portion; a shadow mask suspended closely spaced from the phosphor screen in the panel portion; an electron gun comprising a plurality of electrodes for generating and focusing three in-line electron beams and housed within the neck portion; a deflection device mounted around a transition area between the funnel portion and the neck portion for deflecting the three in-line electron beams in horizontal and vertical directions; and a convergence correction device comprising a plurality of magnetic pieces positioned on opposite sides of each of the three in-line electron beams in an in-line direction of the three inline electron beams and disposed on a phosphor screen side of the electron gun; the plurality of magnetic pieces including a first pair of magnetic pieces positioned on a neck wall side of each of side electron beams of the three in-line electron beams in the in-line direction and a second pair of magnetic pieces positioned on opposite sides of a center electron beam of the three in-line electron beams in the in-line direction; and the first pair of magnetic pieces each having a first pair of protruding portions extending toward an adjacent one of the second pair of magnetic pieces, the first pair of protruding portions of the first pair of magnetic pieces being arranged on opposite sides of a corresponding one of the side electron beams of the three in-line electron beams in a direction perpendicular to the in-line direction; the second pair of magnetic pieces each having two second pairs of protruding portions, one of the second pairs of protruding portions extending toward an adjacent one of the first pair of magnetic pieces and the other of the second pairs of protruding portions extending toward an adjacent one of the second pair of magnetic pieces each of the second pairs of protruding portions of the second pair of magnetic pieces being arranged on opposite sides of a corresponding one of the three in-line electron beams in a direction perpendicular to the in-line direction; and the second pair of magnetic pieces being thinner on a side-electron beam side thereof than on a center-electron beam side thereof.
Further, it is possible to provide a cathode ray tube which can improve the uniformity of resolution over the entire phosphor screen by correcting deflection defocusing corresponding to the amount of deflection, enhance the resolution at the center of the phosphor screen by suppressing the influence of the space charge repulsion with a shortened distance between the phosphor screen and the main lens, can shorten the overall length of the cathode ray tube and can suppress the appearance of moire patterns.
The cathode ray tube of the present invention can make possible a image display device capable of displaying a larger amount of information, reproducing a flickerless high quality image, and making its cabinet thin.